Exception on import if external_id is not a number

[stevenx]

external_id should also be allowed to have a-z 0-9 - /
example of product id from zalando.pl which is common to compare prices to
numer produktu: C1182F00O-C11

https://www.zalando.pl/calvin-klein-underwear-2-pack-skarpety-c1182f00o-c11.html

[stevenx]

Nevermind... Should use offical numbers instead of product number:
At least for Germany EAN / GTIN is required for all products sold: https://www.gs1-germany.de/
https://sellercentral.amazon.de/gp/help/200211450/ref=id_200211450_cont_200426310