This article gives practical points and is not legal advice. When in doubt, have your situation assessed by a lawyer.
Tell the customer you are recording
Let the customer know beforehand that you are recording and why: to make a correct quote. Preferably do this visibly, not only in the small print.
Record the purpose
Only record for a clear purpose, here making a summary and quote. Don't use the recording for anything else.
Don't keep it longer than needed
Audio contains more than you need. It is sensible to delete audio once the text is written up, and the text too after a fixed period.
Choose processors with care
Speech-to-text and AI are often third-party services. Make agreements (a data processing agreement) and check where the data is. Servers in the EU make it simpler.
Arrange the customer's rights
A customer may ask which data you hold about them and ask for deletion. Make sure you can do that quickly.
How Dealnote does it: before recording you tick that the customer knows, audio is deleted after transcription, the conversation text disappears automatically after 30 days (free) or 180 days (paid), storage is in the EU (Frankfurt) and you can download or delete data.