diff --git a/gso/workflows/iptrunk/deploy_twamp.py b/gso/workflows/iptrunk/deploy_twamp.py
index c5b74be3909bf073fa38e416555c5c781df73901..8e2e1016b17fbfc6ba5840e8f47a9c831c9ced17 100644
--- a/gso/workflows/iptrunk/deploy_twamp.py
+++ b/gso/workflows/iptrunk/deploy_twamp.py
@@ -7,9 +7,11 @@ from orchestrator.types import FormGenerator, State, UUIDstr
 from orchestrator.workflow import StepList, done, init, step, workflow
 from orchestrator.workflows.steps import resync, store_process_subscription, unsync
 from orchestrator.workflows.utils import wrap_modify_initial_input_form
+from pydantic import validator
 
 from gso.products.product_types.iptrunk import Iptrunk
 from gso.services.provisioning_proxy import execute_playbook, pp_interaction
+from gso.utils.helpers import validate_tt_number
 
 
 def _initial_input_form_generator(subscription_id: UUIDstr) -> FormGenerator:
@@ -23,6 +25,10 @@ def _initial_input_form_generator(subscription_id: UUIDstr) -> FormGenerator:
         )
         tt_number: str
 
+        @validator("tt_number", allow_reuse=True)
+        def validate_tt_number(cls, tt_number: str) -> str:
+            return validate_tt_number(tt_number)
+
     user_input = yield DeployTWAMPForm
 
     return user_input.dict()