If you have to close the Pixop app after starting an upload, you can come back to it anytime and pick up where you left off in the upload.
Just click the 'resume upload' button and choose the file again.
Here's what that looks like:
You'll find the 'resume upload' button in the lower right-hand corner of the screen:
. . .
P.S. If you run into difficulties or need help, please reach out to us here or at firstname.lastname@example.org — we're always willing to lend an ear 👂