Hi Reggie,
Thank you for writing to us. The limits for 'finalUrlSuffix' field in the API should match the limits in the web interface. There is no maximum limit documented for this field, however a URL has a maximum limit of around 2000 characters before it will no longer function properly in some browsers. So, you might want your URL to be specified within the practical limits. Let us know if you have any further concerns.
Regards,
Nikisha Patel, Google Ads API Team