This is the 146th most frequent Bulgarian word.
просто
"Просто" means "simply" or "just" in English.
In this sentence, "просто" is used as an adjective, meaning "simple".
Това е просто нещо за решаване.
This is just something to solve.
Here, "просто" serves as an adverb, implying "merely" or "simply".
Просто трябва да се отпуснеш.
You just need to relax.
In this context, "просто" intensifies the adjective "incredible," functioning as a qualifier to stress the sentiment.