21656: The ContentVariables Parameter is invalid

Twilio returns this error when your ContentVariables value is invalid for a message request that uses ContentSid. Send ContentVariables as a JSON string of key value pairs that map template variable numbers to substitution values. If a value is omitted, Twilio uses the template's default placeholder value.

• ContentVariables is not a valid JSON string.
• A variable placeholder in the template is malformed, such as {{example}.
• A variable placeholder is empty, such as {{}}.
• The ContentVariables payload is improperly formatted when you send the message.
• One or more variables resolve to null or an empty string at send time.
• A variable value used in the body contains a newline, a tab, or more than four consecutive spaces.

• Send ContentVariables as a JSON string, such as {"1":"coupon_code","2":"docs"}.
• Check every template placeholder and use valid double curly brace syntax. Do not use incomplete or empty placeholders.
• Make sure each variable has a non-empty value when you send the message. Do not pass null or an empty string.
• Remove newlines, tabs, and long runs of spaces from variable values used in the body.
• If you want Twilio to substitute a fallback value, define a default placeholder value in the template before you send the message.

• Using Variables with Content Templates
• Messages resource
• Content API FAQs and Troubleshooting