Can't connect my database well in laravel

i have my database created using mySQl and ready to use but i can't tell laravel what is the foreign keys and what they reference i tried using this way

Schema::table('course', function (Blueprint $table) {
        $table->foreign('weeklyHoursId')->references('id')->on('weekly_hours');
        $table->foreign('gradeSystem')->references('id')->on('grade_system');
    });

but it dosen't work for me and i still getting this error message

 SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`credithourssystem`.`#sql-2494_38`, CONSTRAINT `course_weeklyhoursid_foreign` FOREIGN KEY (`weeklyHoursId`) REFERENCES

weekly_hours (id)) (SQL: alter table course add constraint course_weeklyhoursid_foreign foreign key (weeklyHoursId) references weekly_hours (id)) any help, please :)

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