I love how the hint tells you "producer" is an acceptable word, but when you use it, it's wrong.
They contact the producer. - now accepted.
Can "erreichen" be used in a similar context?
"jemanden (telefonisch) erreichen" means "to get sb. on the phone"/"to reach sb." and is often used in formulations like "Sie erreichen uns (telefonisch) unter 123456." (You can reach us (via telephone) at 123456.)
I used "supplier," and dL accepted it. But I think a supplier and a producer are not identical; is it the case that "Hersteller" can encompass both meanings?
can't this also mean "contact the producer" as in a command?
No, then the word order would be different: "Kontaktieren Sie den Hersteller."
In Afrikaans a " hersteller" is a repairer, not a manufacturer. What is a someone who repairs things called in German?
The repairman= der Handwerker.
I wrote "They are contacting", which was rejected although that phrase is within Duo's definition of the the verb.