The screenshot states the problem clearly:
Maximum execution time of 60 seconds exceeded
Pages have a time limit inside which they need to do their work, otherwise a badly written PHP script could run forever.
This is why importing huge data sets runs into this problem. The bigger the import, the longer it takes, but your server only allows 60 seconds to do this in. You could bump up the limit but that will cause other issues and this might not be possible with your host. Some of the largest imports I’ve seen can take days
Instead, for anything but the smallest imports:
- Split your export into chunks, multiple files at 5MB each, use the WP CLI exporter to do this
- Import via WP CLI, there is no time limit for terminal commands
However for a hosting company, unless you can get access to WP CLI, doing what you’re doing now will not work and there are no workarounds to make the browser importer screen work with medium to large imports. You may even struggle with small imports if it’s shared hosting, and the results will be unreliable. What might work now may fail in a minutes time as the server gets busier and pages load slower