Error code: 1824 Failed to open the refernced table [table exists] - mysql

Question

I'm trying to add a foreign key constraint, but I'm getting [Error Code: 1824: Failed to open the refrenced table 'agent_agent']
the table agent_agent exists in my database, I can't get my head around this issue.
I tried creating the constraint using the graphical mode of mysql workbench and I'm getting the same error.
select * from agent_agent; return the data, so the table exists in the DB but:
ALTER TABLE demande_contact
ADD CONSTRAINT dddd
FOREIGN KEY (agent_id_id) REFERENCES agent_agent(id);
is returning an error 1824.
Edit: Here's the 2 tables DDL
CREATE TABLE `agent_agent` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`matricule` varchar(6) NOT NULL,
`nom_et_prenom` varchar(60) NOT NULL,
`fonction` varchar(60) NOT NULL,
`structure` varchar(60) NOT NULL,
`poste_org` varchar(60) DEFAULT NULL,
`metier` varchar(3) DEFAULT NULL,
`csp` varchar(20) DEFAULT NULL,
`en_activite` tinyint(1) NOT NULL,
`timestamp` datetime(6) NOT NULL,
`updated` datetime(6) NOT NULL,
`user_id` int(11) NOT NULL,
`service` varchar(60) DEFAULT NULL,
`centre_cout` varchar(10) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `agent_agent_user_id_bfcb5c50` (`user_id`)
) ENGINE=MyISAM AUTO_INCREMENT=628 DEFAULT CHARSET=utf8
CREATE TABLE `demande_contact` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`telephone` varchar(40) NOT NULL,
`agent_id_id` int(11) NOT NULL,
`demande_id_id` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `demande_contact_demande_id_id_0abc00b0_fk_demande_d` (`demande_id_id`),
KEY `agent_id_id_constraint_idx` (`agent_id_id`),
CONSTRAINT `demande_contact_demande_id_id_0abc00b0_fk_demande_d` FOREIGN KEY (`demande_id_id`) REFERENCES `demande_demandetransport` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8