Hi @jody_leonard,
Try to use Google sheets, that's the most widespread format nowadays for import/export. As Excel has different versions and they may have some significant changes between each other. I agree with extra-data it may add. So the best way to use the latest Excel version or Google sheets to avoid a possibility that older Excel versions may cause incompatibility issues.
At Firebear most of our clients use Google sheets as a source.
Btw, what solution you use for import/export jobs?
Thanks.