Product and version
FileMaker Pro Advanced 18.104.22.1684 (also FMPA 22.214.171.1240)
OS and version
MacBook Pro (15-inch, 2018)
2.2 GHz Intel Core i7
16 GB 2400 MHz DDR4
Intel UHD Graphics 630 1536 MB
Labelary has an API to convert Zebra's ZPL printer language into PNGs or PDFs. The expected response from the API is either a PNG or PDF file, depending on the cURL header. When the Insert from URL target is a variable, the script step produces error 507 and no change is made to the target variable. This may be related to the issue reported here: Some URLs produce a false 507 ( validation ) error on Insert From URL
How to replicate
Simply use Insert from URL with the target being a variable and the URL being "http://api.labelary.com/v1/printers/8dpmm/labels/4x6/0/^XA^FO50,50^GB100,100,100^FS^XZ". This will produce error 507.
I've also attached a working demo of the issue. Just press either of the "Get Image" buttons. One button works because the target is a field. The other button produces the error because the target is a variable.
Use a field target instead of a variable.