Why this matters
If people cannot find something, it might as well not exist. A mobile money service may offer bill payment, but if it is hidden under a menu called "Financial services" that nobody opens, customers will think it is missing and go elsewhere. Information architecture, often shortened to IA, is the skill of organising and labelling content so people find it without thinking hard. Several design adverts list it directly.
The main ideas
Group by how users think, not how the company is organised. A bank may have separate teams for cards, loans and savings, but a customer thinks "I want to send money" or "I want to see my balance". Organise around the customer's tasks.
Use the user's words. Companies love internal terms like "Merchant disbursement" or "Value added services". Users say "pay a shop" or "buy data". Your research notes and interview quotes are full of the right words, so use them. If people mix English and a local language, notice which words they keep in English, such as "MoMo", "credit" or "data".
Keep the top level short. On a phone, show the few most common tasks first. Put rarer things one level down. A long list of equal options makes everyone read everything.
Be consistent. If you call it "Send money" on one screen, do not call it "Transfer" on the next.
Card sorting: a simple IA method
Card sorting lets users show you how they group things.