In proper Ayambil, tea is not allowed.

Ayambil means:

• Only one very simple, bland meal in the day
• Generally no milk or milk products
• No ghee/oil
• No sugar/sweets
• Very limited or no spices
• No stimulants like tea / coffee / chocolate

Tea usually has:

• Taste (rasa) and stimulation (it excites the mind)
• Often milk and/or sugar

So it goes against the basic purpose of Ayambil, which is to reduce attachment to taste and keep the body–mind very simple and calm.

Both Śvetāmbara and Digambar traditions follow the same main idea: Ayambil is nirāsa / almost tasteless, non‑indulgent food. So tea is normally avoided. If someone has health issues, they should speak to their guru/pravachankar and take a proper pachchakkhān (vow with conditions).

You can read more about Ayambil here