Take, for example, Sohrab Mostaghim, 28, and some of his friends, all graduates of Tehran’s best universities, who designed a treasure hunt set in the city’s most popular park. Soon, hundreds of people were happily paying the equivalent of $11 each to play the game, based on riddles and questions embedded in an app on their mobile phones.

But when they told a manager of the park what was going on, they were blindsided by his reaction.

“Instead of welcoming the extra visitors and this fun game, he pressured us, claiming our promotional video was against Islam, since at the end the brother and sister hug,” Mr. Mostaghim said. Physical contact between men and women in public is officially forbidden in Iran, but the rules are widely flouted in the larger cities.

Ultimately, the partners felt they had to shut the game down, whereupon the manager changed his tune.

“Now, he is asking us for bribes to allow us to use the park,” Mr. Mostaghim said. “We are not even sure if he will really allow us if we pay.”

The whole idea of a start-up is to embrace freedom to think and create, he said, “but we don’t have that here.”

Even established businesses that suffered during the years of sanctions are finding it difficult to recapture lost customers. For Bahram Shahriyari, 58, the prospect of lifting international sanctions after the nuclear deal was a faint light at the end of what had become a dark tunnel.

Until the sanctions were imposed, he had owned a business providing parts and components for new and used vehicles made by Peugeot-Citroën of France, one of the most prominent foreign brands in the country. At its peak just four years ago, his company had 400 employees and even exported parts to France.