User defined variable in the stored function

[Alex Graham]

Hello guys.
I have this stored function
----
CREATE DEFINER=`root`@`localhost` FUNCTION `horw`(Y DOUBLE, n DOUBLE,alpha DOUBLE,t JSON) RETURNS double
READS SQL DATA
DETERMINISTIC
BEGIN

RETURN t;
END
---
and stored procedure
---
CREATE DEFINER=`root`@`localhost` PROCEDURE `Estimation_Methods`()
BEGIN
declare Y DOUBLE;
declare n DOUBLE;
declare alpha DOUBLE;
declare t CHAR;
SET Y=10000000;
SET n=56;
SET alpha=0.05;
SET t = '[1,2]';
SELECT horw(Y,n,alpha,t);
END
---
So I have json array as a variable in the function.
When I call the procedure with t I get Error Code: 1406. Data too long for column 't' at row 1
I also tried using @t in the procedure, no result.
What the data type should I need to use in the stored function for json array t?
Regards,