"I tried one more time."
Translation:Jeg forsøkte en gang til.
"Å prøve" has two main definitions:
1: to test, try, control, investigate (alt. verbs: "å teste" (I, II), "å kontrollere"(III), "å undersøke" (IIII))
"Vi har [prøvd/testet] [/ut] det nye kurset."
"We've [tested/tried out] the new course."
"Har du [prøvd/smakt] fisken?"
"Have you [tried/tasted] the fish?"
2: to try, attempt, seek (alt. verbs: "å forsøke" (I, II), "å søke" (III))
"Vi har [prøvd/forsøkt] å fullføre det nye kurset."
"We've [tried/attempted] to finish the new course".
"Jeg skal [prøve/forsøke] å slå rekorden."
"I will [try/attempt] to beat the record."
"Å prøve lykken"
"To try one's luck"
"Å forsøke" only covers the second definition (and would not be preferred in the case of its third example sentence), while "å prøve" actually has two additional definitions not mentioned above.
I'm writing this with the intention of giving sakerrison' greater insight into the nuances of Norwegian grammar.
Norwegian quantifiers are split into two groups: those that are used with Countable (Norwegian – Tellelig) Nouns, e.g., friends; cars; books; etc. and those that are used with Uncountable (Norwegian – Utellelig) Nouns: e.g., sand, beer, milk, water, knowledge, evidence, confidence, etc.
Quantifiers that are used with Countable Nouns include: mange; flere; noen; få; alle; and, ingen.
Quantifiers that are used with Uncountable Nouns include: mye; mer(e); noe; litt; lite; and, all (alt).
The answer to your query is “mer” cannot be used with Countable Nouns. The Norwegian sentence can be translated: "I tried once more." In English one could say, "I tried twice more"; "I tried thrice more" (now a bit archaic) or "I tried another three times" and so on.
"Mer" can be used as follows: "Jeg vil ha mer melk." But, "en til" would have to be used, as shown, in response to the question, "Vil du ha mer melk?" "Ja takk, jeg vil gjerne ha et glass til."
I hope that helps.
Trying to think why 'mer' might not be accepted in a translation here, but struggling to come up with an answer to distinguish from 'til' that is given.