I am pretty sure this is a bug and have contacted Formidable Support about it.  I have a form that has a repeater in it and a signature field outside of the repeater.  I have an API post action to send this data to another form.  The receiving fields match with the sending fields, except the signature is sent to a text field as that's the only way to transfer the signature to a field in another form.  The data all shows up in the destination form unless you choose to draw the signature instead of type it.  The Formidable Log shows the action ends in a 400 error if you draw a signature.  Also if you don't transfer any repeater data, a drawn signature will be transferred to the destination field just fine.

I'm trying to come up with a work-around but the only thing that looks like it could work is PHP.  However the value transferred is serialized.  Any suggestions for a work around?   The attached text file shows an example of the serialized data for a drawn signature.  An example of the one for the typed signature is much shorter (signature is "Jane"):  a:3:{s:7:"content";s:4:"Jane";s:5:"typed";s:4:"Jane";s:6:"format";s:5:"typed";}.