"Julia takes the tea from Peter and gives it to Raj."
Translation:जूलिया पीटर से चाय लेती है और राज को देती है।
My answer: "जूलिया पीटर से चाय लेती है और वह राज को देती है।" Marked wrong for including the "वह", it seems. Can any one clarify whether this use of a pronoun is invalid in Hindi, or whether I just used the pronoun the wrong way? Or is this sentence right, and Duo just wasn't prepared for it?
I presume you want to वह to refer to the 'tea' (like 'it' in the original sentence)? In that case, since it is the object, you have to use the उसे form. 'जूलिया पीटर से चाय लेती है और उसे राज को देती है'.
On the other hand, if the वह is supposed to refer to 'Julia', then the placement is right. But if you're specifying that the subject is 'Julia' again, you also need to specify that the object is 'tea'. The sentence would then be 'जूलिया पीटर से चाय लेती है और वह उसे राज को देती है' where वह refers to Julia and उसे to the tea.
Another option is to make the 'tea' the direct object of देती too just as it is to लेती - जूलिया पीटर से चाय लेती है और राज को वह चाय देती है.
The direct object of a verb needs to be placed as close to the verb as possible (right before it or before words like नहीं which have to be placed right next to the verb). Here चाय is the direct object of लेती so it needs to come after पीटर से.
That said, your sentence would not be unnatural in spoken Hindi when spoken with the right inflexion.