tl;dr: Both are grammatical, but it depends on what you intend to say. In this case it depends if the time of the request in relation to the utterance is pertinent or not.
Firstly, there are three grammatical categories bound up in your example sentence.
- Tense - When in time the event occurred
- Aspect - Whether the event is complete (perfect aspect) or not (unmarked form)
- Voice - Whether the event is described from the perspective of the agent (active voice) or the patient (passive voice)
So, let's take a sentence such as your team requests the items. The event being denoted is request, it requires an agent, your team and a patient, the items. As the sentence is active, the agent is encoded as the subject and goes before the verb phrase, and the patient is encoded as the object and is encoded within a verb phrase as a complement of the verb. The tense is present and it is unmarked for aspect.
You can do various things with this sentence. You can change the tense to past by request -> requested, and you can change the aspect to perfect by requests -> have requested. Note that this is still technically present tense (or non-past depending on your theory of tense in English), and what's important here is that the event, the requesting, is complete, rather than its relationship in time with the time of the utterance. You can then change the tense of this by have requested -> had requested. In this case, the event is complete, and took place at some time in the past as compared with the utterance. The context of this might be I came by yesterday, and your team had requested the items already.
Another thing you can do is change the voice so as to focus on the patient rather than the agent. This is a more complex syntactic transformation. You take the patient, the items and make it the subject, and you take the agent, your team and you either delete it or you put it into a prepositional phrase headed by by, and you change the verb from [verb] to [be + verb-en], so, from request to be requested. Then, the auxiliary verb be is put into the right tense. So for present, you get the items are requested (by your team).
Next step is combine past tense with the passive, producing were requested. Alternatively, you can combine the passive with perfect aspect, producing have been requested.
Lastly, you put all three together and you get had been requested.
Thus, the difference between have been requested and had been requested is simply one of tense. The former is present and the latter is past. You woulduse the former where the time of the request itself is not pertinent, but instead the fact that the requesting is complete. You would use the latter if the time of the request is in fact pertinent, such as in the context I came by yesterday with the request form, but the items had already been requested by your team, or somesuch.
Just a note, I don't mean to imply that past perfect passives are 'transformed' from unmarked or default structures by movement. But it's a helpful way of thinking about it.
I'm also skipping a lot in here, such as that perfect aspect is encoded by [have + verb-en], but if I get any more complicated I'm-a hafta pull out some tree diagrams!