Foreign key constraint is incorrectly formed

create table in_sync_data_source

(

   ds_oid               integer not null auto_increment,

   dbms_name            varchar(256) character set utf8mb4 not null,

   server_name          varchar(256) character set utf8mb4,

   cluster_id           varchar(256) character set utf8mb4,

   database_name        varchar(520) character set utf8mb4,

   logid                varchar(256) character set utf8mb4,

   owner_oid            int,

   root_rs_oid          int,

   readonly_ind         tinyint not null,

   ctrl_ins_dtm         timestamp(6) not null default current_timestamp(6),

   ctrl_upd_dtm         timestamp(6) not null default current_timestamp(6) on update current_timestamp(6),

   ctrl_usr_id          varchar(256) character set utf8mb4 not null,

   primary key (ds_oid)

);

create table in_sync_object

(

   rs_oid               int not null,

   ds_oid               integer not null,

   object_cat           varchar(520) character set utf8mb4 collate utf8mb4_bin,

   object_schem         varchar(256) character set utf8mb4 collate utf8mb4_bin,

   object_name          varchar(256) character set utf8mb4 collate utf8mb4_bin not null,

   object_sig           varchar(512) character set utf8mb4,

   object_subtype       varchar(60),

   object_ignore_ind    tinyint not null default 0,

   ctrl_ins_dtm         timestamp(6) not null default current_timestamp(6),

   ctrl_upd_dtm         timestamp(6) not null default current_timestamp(6) on update current_timestamp(6),

   ctrl_usr_id          varchar(256) character set utf8mb4 not null,

   primary key (rs_oid)

);

create unique index IX1IN_SYNC_OBJECT on in_sync_object

(

   ds_oid,

   object_cat,

   object_schem,

   object_name,

   object_sig

);

-- [10.9.3-MariaDB]Can't create table `in_sync_object` (errno: 150 "Foreign key constraint is incorrectly formed")

alter table in_sync_object add constraint FK_IST_ISDS_DS_OID foreign key (ds_oid)

      references in_sync_data_source (ds_oid) on delete restrict on update restrict;