The insert/update operation attempted to write data that was too large for a column in your MySQL table.
@AppSheet: Please show what column actually causes this error.
This is just for people running into the issue where AppSheet wants to save a base64 string to your database instead of saving the image (or siganture/drawing) to Google Drive.
This is most likely a fallback mechanism but not documented anywhere.
If you run on MySql you will probably have to change the column to text in order to get syncs through. Then make sure you upgrade your storage on Google Drive.
Once that’s completed, you can manually convert the base64 strings to images, change the the entries to represent the path to the manually created file and revert back to your original column type (probably varchar(255)).
You can use this page to decode your base64 strings.
I hope that will help someone to solve their problem.