If you try uploading to Endomondo from my apps, you will probably experience a failure. This is due to an update on the endomondo side, which involves various changes (remember: Endomondo support is in permanent beta). Most of those changes are trivial (some endpoints previously on http have been moved to https).
One of those change is big and breaking, as they have configured their servers so that SNI (server name indication) is required during the HTTP negotiation (this is unusual for a big company, as it's mostly the case for shared hosting; might be a configuration problem on their side). Unfortunately, the android library classes that I need to use to send data to endomondo do not support SNI (in case you're wondering: browsers like chrome under android don't use the library classes :-).
I already have a workaround , and I'm currently testing it. I may have a release ready later today or maybe tomorrow. Still, the patch requires that I reach down to some hidden parts of the system to enable SNI. It may or may not work on your android device, that is, if the manufacturer has messed too much with the standard distribution, it may still fail.
If, after I release a new version (Sportablet 6.9 / Uploader for Garmin 6.1), you find that you still have problems, please get in touch using the contact page, I'll need to see your transfer logs.
Meanwhile: if you want updates on this issue, please follow the sportablet account on twitter or facebook.