developing would be "desarrollando", the infinitive, while sometimes can mean the -ing version of the word, here it is literally To Develop (Infinitives carry/imply the additional word "To" when converted to english) Try and translate the spanish as literally as possible instead of paraphrasing the english. This is a common, heart-losing, mistake seen often on DL.
Don't bother. The DL is correct.
Among other things, "para" means "in order to (or for the purpose of) : develop. It is followed by an infinitive in these situations.
This is a VERY common Spanish construction.
Don't try to translate "literally" (whatever that means).
See this DUO tip, which y'all must have missed. https://www.duolingo.com/skill/es/Activities-3/tips
Quote from the tip:
When para is followed by an infinitive, it’s usually used to talk about the purpose for doing something.
Estudio mucho para encontrar un trabajo bueno. (I study a lot in order to find a good job.)
Necesitamos encontrar la llave para abrir la puerta.
We need to find the key [in order] to open the door.
I believe you are mistaken.
Gigi's answer is correct and sounds better than Duo's answer to my American ears.
In Spanish "verbal nouns" are always infinitives--never the gerundio (the present participle).
In English, we use both infinitives and gerunds (-ING verb forms --the English present participle acting as a noun).