Vendors describe migrations as straightforward. Engineering teams who have run one describe them differently. The gap between those accounts is where projects slip.
If your scheduling vendor is consolidating regions, deprecating a product, or changing terms you cannot accept, you are facing this work whether you switch vendors or stay. That is the part worth internalising early: a forced regional migration and a vendor change can involve many of the same operational tasks. Depending on the migration, both may require re-authentication, identifier remapping, endpoint changes, and updates to webhooks or SDK configuration. If you already have to absorb migration work, it may be worth evaluating whether staying with the same vendor or switching creates the better long-term outcome.
This is a realistic account of the work.
What you are actually moving
Scheduling integrations look small until you inventory them. Four things are in scope, and they carry different levels of difficulty.
Access grants. Every end user who connected a calendar did so through an OAuth flow tied to your old vendor’s application. Those grants do not transfer. Users reconnect. This is the hardest part of any migration, and it has nothing to do with code.
Identifiers. Vendor-specific identifiers may change during migration. Event IDs, calendar IDs, account or grant IDs, and other stored references may need to be remapped or reconciled in your application. Anywhere your application stored a vendor identifier in your own database, you need a mapping strategy.
Configuration. Availability rules, buffer times, booking page settings, notification templates, conferencing defaults. Often straightforward to recreate, but easy to underestimate because configuration may be spread across dashboards, code, and undocumented operational settings.
Integration surface. Webhook endpoints, SDK configuration, API base URLs, retry logic, rate limit handling. Mechanical, and the part your team is best positioned to estimate accurately.
Phase one: inventory, roughly one week
Before any code, answer four questions.
Where does the old vendor’s identifier appear in your schema? Grep for it. Teams routinely find it in places nobody remembers writing, particularly analytics events and support tooling.
How many end users hold an active grant, and how many are actually active? The reconnection problem scales with the first number, but your urgency scales with the second. A long tail of dormant grants can often be retired rather than migrated.
What does your own contract say? If your customer agreements contain data residency, subprocessor, or change-notification commitments, a vendor change may trigger contractual review or customer communication requirements. Involve Legal or Privacy early rather than discovering those obligations during cutover. This has a longer lead time than the engineering work, and it is the item most often discovered late.
What data can you export or retrieve from the existing platform, in what format, and for how long after termination or cutover? Confirm the format before you need it, not during cutover.
Phase two: parallel build, one to three weeks
Run both integrations at once. Do not cut over cold.
Provision against the new vendor, wire up webhooks to a staging endpoint, and validate sync behaviour against a small set of internal accounts. What you are testing for is the semantic differences: how recurring events expand, how cancellations propagate, how all-day events handle time zones, how conferencing links get attached. Calendar providers and APIs can differ in how they represent recurrence, cancellations, all-day events, time zones, and conferencing. Those differences can surface as customer-visible bugs if you do not test them explicitly.
Build your identifier mapping table in this phase. Old ID to new ID, populated as grants get created. It is unglamorous and it prevents most of the data integrity problems that show up later.
With Nylas, data residency is selected when an application is created. U.S. and European applications use different regional API endpoints, and the region cannot simply be changed on an existing application. If you are migrating regions, plan application creation, authentication, grant migration, webhook configuration, and SDK endpoint changes before cutover. Details in the data residency documentation.
Phase three: user reconnection, two to eight weeks
This phase is less about code than adoption, communication, and customer behavior—and it may dominate the elapsed timeline.
Your users have to reauthorize. Some will do it the day you ask. Some will do it after the fourth reminder. Some never will, and you need a decision in advance about what happens to those accounts.
Common approaches include: an in-app prompt at the point of use, a clear explanation of why reconnection is required, a meaningful deadline, and graceful degradation for users who have not yet reconnected.
Relying only on a single announcement email and a hard cutoff creates avoidable support and adoption risk. Expect a support spike regardless and staff for it.
If you serve businesses rather than individuals, sequence by account rather than by user, and give your largest accounts a heads-up before the prompt appears. Admins dislike learning about a reauthorization campaign from their own users.
Phase four: cutover and decommission, one week
Route new bookings to the new integration first, keeping the old one live for existing grants. Once reconnection reaches a threshold you have decided in advance, flip reads. Where contract terms and cost permit, keep the legacy integration available for a defined validation period before termination. The goal is to confirm that new bookings, historical references, notifications, and edge cases behave as expected before the old environment becomes unavailable.
Confirm the vendor’s post-termination data handling and deletion process, and retain appropriate evidence where required by your contracts or internal governance program.
Realistic totals
Actual timelines vary significantly based on architecture, user population, authentication model, contractual review, and migration scope. The ranges below are planning examples rather than delivery commitments.
Scenario
Engineering
Elapsed
Simple booking flow, few hundred users
2 to 3 weeks
4 to 6 weeks
Embedded scheduling, thousands of users, B2B accounts
4 to 6 weeks
8 to 12 weeks
Multi-region, enterprise customers with contractual terms
6 to 10 weeks
12 to 16 weeks
Engineering is the smaller number in every row. Elapsed time is dominated by user reconnection and, in the third row, by your customers’ own legal review. Plan against elapsed.
Where the boundary sits
Your team owns
Areas Nylas can help with
Schema changes and identifier reconciliation
Calendar/provider behavior and integration design
Reconnection UX and customer communications
Authentication and regional application setup
Dormant-account migration decisions
Webhook architecture and configuration
Your contractual/customer obligations
Technical validation and migration planning through available support or Professional Services
Nobody can do the reconnection for you. Any vendor claiming otherwise is describing a different migration than the one you are running.
One decision worth making deliberately
If you are migrating because your vendor changed regions, you are absorbing the cost of a decision you did not make. It is worth asking what happens the next time they make one.
That is not automatically an argument for switching vendors. It is an argument for evaluating switching costs while migration work is already underway. If the same authentication, data mapping, integration, and customer-communication work would be required later, understanding the alternatives now can help avoid making a short-term infrastructure decision without considering its longer-term consequences.
If you want to work through the sequencing against your own architecture, talk to our team.
Email and Contacts API 
Calendar API & Scheduler 
Notetaker API 
Agent Accounts 
Sales & CRM 
Recruiting & ATS 
Healthcare
Financial
Legal
Real Estate
Education
Field Services
Docs
SDKs
Guides
Integrations
API status
Changelog
Support
Enterprise
