Always use E.164 format — digits only, with country code, no formatting characters.
Example
Correct
17145551234
Wrong
(714) 555-1234
Wrong
+1-714-555-1234
Wrong
714-555-1234
Strip all non-digits and prepend the country code (e.g., 1 for US). The Create Lead endpoint will auto-prepend 1 if you omit the country code, but all other endpoints require the full E.164 format.
