Define the source of truth first
Decide which database owns the member record, which field defines expiry and how duplicates, manual entries and cancelled accounts should be handled.
Passwords need a deliberate plan
Old platforms may use different hashing methods or store passwords in ways the new application cannot accept. Decide whether you can migrate hashes safely, support a temporary compatibility path or require a reset.
Preserve the dates that matter
An account creation date is not the same as a membership expiry date. Make sure the business rule is written down before data is transformed.
Test access before the final cutover
Use representative users: active, expired, manually added, different plans and edge cases. The migration is only successful if the right content and account actions work afterwards.
Communicate clearly
Members should know what is changing, whether they need to reset a password and who to contact. Support planning is part of the migration, not an afterthought.
We can look at the real website with you.
If the issue is already affecting your business, send us the URL and what is happening. We will help you work out the most sensible next step.