I filed the petition to reopen the question, so I reckon I should try and present a more compelling defence of it.
In the alleged duplicate the OP thinks the correct phrase is Carreteiros em + verb, which he knows is spelled with a j. Someone has told him elsewhere (see his first comment to his own question) he is wrong (he is), and he came to us to ask for our view. So this is a grammar question, whether noun + em + verb is a grammatical construction. The allegedly original question is about spelling and does not address this issue. Now I’ll try and back up each individual point.
The OP knows the conjugations of the verb viajar are spelled with a j. He writes (first line, third paragraph): “a regra onde diz que é para usar com a letra J quando é verbo.” So this is what the allegedly original question clarifies, but the OP knows this already.
The OP thinks em + verb is grammatical. He writes (third paragraph):
“[E]u tenho um sujeito na terceira pessoa do plural ( carreteiros ) fazendo uma ação viajar o em viajem.
and, even more explicitly, in the following statement, where he thinks guerra is a verb:
"Soldados em guerra" onde o em esta ligando um verbo guerrear
In his comment to my answer to his qestion he acknowledges that then, after reading my answer and a few comments to his own question and my own answer, he understood that guerra is not a verb (he says “realmente não da p/ conjugar ‘eu guerra, ele guerra’”). And from this he understood that carreteiros em must be followed by a noun and not a verb.
So I think this makes clear that his doubt was about grammar not spelling. The answers to the other question do no address his doubt, nor is there any reason why they should. Math might have included the example carreteiros em viagem in his answer. But, first, why should he? Among all the thousands of examples one can build with the noun viagem? Second, even if he did include this example, it would still not explain to the OP’s satisfaction why you should have em + noun viagem rather than em + verb viajem. It would only reiterate what someone else had already told him, that the correct form was carreteiros em viagem (see his comment to his own question). But he did not understand why that was the case. So he would need to ask a new question. That’s what he’s done.