Enketo submission error

My project has been working smoothly however, one enumerator is having issues submitting responses collected from the field.

According to the enumerator data was collected offline but has however been unable to submit upon internet connection.

The attached image is the message that comes up when he attempts to submit.

I am also informed that he uses phoenix (browser)

Can you kindly help with an alternative approach to retrieve the drafted responses? or best means to upload/submit the data to the server.

NB: Minded by geographical barriers.

Welcome to the community, @cerathdev! Would you mind advising your team to use modern browsers such as Chrome, Firefox, Edge` etc.? These browsers should not have such issues. Besides, please also advise them to update these browsers to it’s latest version (for best results).