# KERIOX TDA app notification system ```plantuml actor "Actor 1" as a1 participant "Witness 1" as w1 box "TDA" #LightBlue participant "App" as tda2 participant "KERIOX" as k1 end box actor "Actor 2" as a2 a1 -> w1 : Sends delegation request\nto mailbox of Actor 2 w1 --> a1: ACK w1 -> w1: Processes delegation request\nand stores it in the Actor 2\nmailbox w1 -> tda2: Notify via Firebase\nabout new msg in mailbox tda2 -> tda2: Process notification\nreceived from Firebase tda2 -> tda2: Show prompt in device UI\nand inform user via\n"New pending activity" msg tda2 <- a2: user clicks on prompt\nand is being redirected\ninto TDA app tda2 -> k1: Runs `poll_mailbox_msgs` fn k1 -> w1: Queries witness for new\nmessages stored in mailbox k1 <- w1: New messages k1 -> k1: Processes new msgs k1 -> k1: Stores msgs on KERIOX internal stack\nthat require user digital signature tda2 -> k1: Periodically runs\n`get_signature_required_msgs`\nfn tda2 -> a2: For each msg, sign message tda2 <- a2: Signed msg tda2 -> k1: Add signed msgs k1 -> w1: Sends IXN event as a confirmation of delegation\nto Actor 1 mailbox ```