Hi, i am seeking some helps from the experts here in the community. i am not sure that is feasible with the current checkout extensibility feature of shopify. i would like to do some input validation in the checkout form. in the default contact input field (which only accept either phone or email) , i would like to only allow phone instead of email. any possible solution to achieve that ? I have tried to work with some extension app to do some checking before the form submission. but i could not get the input value via the APIs provided. (useAttributes)
Topic summary
A user wants to modify Shopify’s default checkout contact field to accept only phone numbers instead of allowing both phone and email. They attempted using extension apps with validation checks before form submission but couldn’t retrieve the input value through provided APIs (useAttributes).
Key constraint identified:
- Checkout extensibility is only available for Shopify Plus plans
Suggested solutions:
- For Plus stores: Use Shopify’s Checkout Blocks app
- For non-Plus stores: Collect this information at the cart step before checkout
- Alternative: Find third-party apps with similar functionality
Status: The question remains open, with a request for the original poster to provide more details about their current implementation and code.
Hi @lskjames 
only stores on a shopify Plus plan can use the checkout extensibility.
For such stores try shopifys checkout blocks app https://help.shopify.com/en/manual/checkout-settings/checkout-blocks
Otherwise find similar apps
Plans not on shopify Plus need to collect such info at the cart step before checkout.
Beyond that you’d drastically need to improve the quality of your question showing your current work.